The first credible mention of Christmas on this date comes from an early Roman calendar from around 336 AD. Emperor Constantine, the first Christian ruler of Rome, was likely behind this, but it wasn’t until a decade or so later that this date would become official, thanks to Pope Julius I.

Julius served as the Bishop of Rome for 15 years in the first half of the 4th century, and unlike Constantine has mostly been forgotten. But his decision to declare December 25th as Christmas has remained unchanged for over a millennium and a half, having a deep impact on billions of people and depriving poor journalists of getting to write easy articles asking, ‘when is Christmas this year’, as they often like to do for Easter and Mother’s Day.